In our introduction into the Pi (𝛑) of a circle we have learnt that the relationship between the circumference of a circle and its diameter is always more than 3.

A more accurate result has been given as 3.14, and most calculators may have a key for 𝛑.

We can understand that the circumference is also called the perimeter of a circle. This is because perimeter is the distance around an object.

The diameter is twice the radius.

Out of the ratio between the diameter and the circumference (𝛑 = c/d), we can have the following formulae:

Circumference = 𝛑 x diameter (2r)

OR

Circumference = 𝛑 x 2r

SO

Circumference = 2 𝛑 r

Below is a video on the above explanation.

The next video is a tutorial on how to calculate circumference given the diameter, and vice versa.